In order to protect an animal against an invading pathogen (bacterial, viral or parasite) it is often advisable to vaccinate the animal with the whole organism or with such subunits of the pathogen as to elicit a protective immune response in the host. The immune response generated to such antigenic challenge can often be augmented by the co-administration of an immunopotentiating agent or adjuvant. The best of these agents are the depot type adjuvants (such as Freund's complete adjuvant, Freund's incomplete adjuvant and montanide). These adjuvants are capable of increasing the antibody response after antigen injection to some 50 to 100 times the level obtained with antigen injected alone.
Whilst adjuvants such as Freund's complete adjuvant, Freund's incomplete adjuvant and Montanide can greatly enhance the immune response to an antigen, they suffer from some disadvantages. When used with an antigen in an injectable form, large lesions often form at the site of injection, a situation which renders them unsatisfactory for such use in humans, pets or in meat animals. Furthermore, these adjuvants fail to act as immunopotentiating agents when administered orally or enterally.